[POWERPC] 4xx: Add endpoint support to 4xx PCIe driver

This patch adds basic endpoint support to the 4xx PCIe driver.

This is done by checking the device_type property of the PCIe
device node ("pci" for root-complex and "pci-endpoint" for endpoint
configuration).

Note: Currently we map a fixed 64MByte window to PLB address 0 (SDRAM).
This should probably be configurable via a dts property.

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>